General Linux Commands

cat
Dumps a file's contents to stdout.

clear
Clears the terminal and leaves you with a clean and fresh
prompt at the top. Often in .bash_logout files so that
the person who sees your terminal after you cannot see
what you were doing just before you logged out.
See also: ^l

reset
Resets the terminal. Good for when you mess it up by accidently
cating binary data to it.

tail
Outputs the last 10 lines of a file.
-n 100 will output 100 lines.
tail -f file will hold the file open
and keep the contents dumping to the screen as the file is added
to. Perfect for watching log files.